"Halliwell was familiar with York - his father lived in Huddersfield - and the description of Claudia's murderer is identical to him - a left-handed smoker, 5ft 8-10in, with slightly receding hair and a skinny build.

"Claudia was reported missing from her home on March 19, 2009 - exactly two years to the day before Sian. It is also the same date that a woman called Linda Razzell disappeared."

Karen's claims about Halliwell and his possible involvement in Claudia's murder are supported by the senior detective who bought him to justice.

Former Detective Superintendent Steve Fulcher told the Sunday Express: "Claudia Lawrence disappeared from York seven years ago. Halliwell's father lived a few streets away from where Claudia went missing.

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"It fits his pattern of behaviour - abducting women walking alone either late at night or early in the morning."

Karen's "extremely painful journey" began on March 24, 2011, when police discovered the body of Sian O'Callaghan, a 22-year-old from Swindon who had gone missing.

For nine years, Karen did not know the fate of her daughter - she had run away from home after descending into a world drugs and prostitution.

11 days after she saw the news about Sian on television, police confirmed they had also found Becky's remains.

Karen, who lives with her second husband Charlie, a businessman, and has a son Steven, said: "I had a gut feeling it was Becky. Call it mother's instinct. She had been missing too long.

Karen also thinks Halliwell murdered Melanie Hall who disappeared from a Bath nightclub in 1996 but whose remains weren’t found until 2009

But the father-of-two has won praise from Karen who said that her daughter's remains may never have been found if it was not for his actions.

Fulcher has subsequently criticised police forces for "obsessing" about procedure rather than looking at the bigger picture and said he wants to ensure detectives in a similar position are not treated in the same way he was.

When the trial was abandoned, Karen launched a Justice for Becky campaign, taking her petition to Downing Street.

Since then, she has amassed boxes of evidence - stored poignantly in her daughter's old bedroom.

Karen believes that as well as Claudia Lawrence, Halliwell may have killed 23-year-old prostitute Sally Ann John, who was classified as a missing person in 1995.

She said: "She was a Swindon girl and knew him well. She used to live in the same street as Halliwell, baby-sit his kids and take his taxis.

Linda Razzell is another woman that Karen suspects Halliwell murdered when she disappeared in 2002 after dropping off her children at school

Karen also believes he was involved in the murder of Melanie Hall, who disappeared from a Bath nightclub the following year in 1996.

"She was taken by an unmarked taxi", said Karen. "He has to be in the frame."

Melanie's remains were found in vegetation beside the M5 at Thornbury over a decade later in 2009.

Karen's thoughts on Melanie's disappearance are also shared by Fulcher, who now works as a security consultant in Somalia, who said: "The circumstances match his modus operandi in abducting a girl, late at night, from a nightclub. Evidence of her being tied up with rope is consistent with Halliwell's interests."

Finally, Karen is also convinced that Halliwell is responsible for the murder of Linda Razzell, who disappeared on March 19, 2002, after dropping her children off at school and driving into Swindon town centre.

Her husband Glyn was convicted of her murder but has always protested his innocence.

Karen and her family pay respect to Becky at the field where her body was found

Karen added: "Halliwell was besotted with Linda. He first met her in 1998 when he dug the footings on her property and used to stalk her. He used to sit in his taxi and watch her walk to work through an alleyway - they later found her mobile phone there. He even used to sketch pictures of her.

Karen also believes Halliwell has raped and beaten many more women.

"During my campaigning, I uncovered numerous stories which I passed on to the police of girls who had lucky escapes in the back of his taxi.

"He drove one girl who got into his taxi to a wooded area, which terrified her, and she screamed.

"It was only after he was disturbed that he drove her back to Swindon.

"Quite a lot of the people I encountered have given statements to the police so hopefully Halliwell will face more charges."

Speaking just hours after he was sentenced to life, she said: "The next fight is for the families of other missing women, whose bodies may lie in shallow, unmarked graves.

"Halliwell represented himself like Ted Bundy and I only hope that if he killed as many people as Bundy, we find out sooner rather than later."

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